1. Field of the Invention
This invention relates to an exhaust gas treatment apparatus that includes a water vortex means and a discharge pipe and particularly to an exhaust gas treatment for treating exhaust gases generated in diffusion and deposition processes.
2. Description of the Prior Art
In semiconductor manufacturing process, a blank wafer has to go through hundreds of processes to equip it with function desired. The processes include diffusion, deposition, (particularly chemical vapor deposition, or CVD), etching and the like. These processes mostly require large amount of reaction gases, especially in the diffusion and deposition processes. While a small portion of the gases have reaction with the wafer, a great portion of the gases do not have reaction with the wafer and become exhaust gases. The exhaust gases mainly include SiH.sub.4, SiH.sub.2 Cl.sub.2, etc. They are highly toxic and should be properly treated to remove the toxicity to comply with industry standards before being discharged out.
In the semiconductor industry nowadays, a commonly used treatment method for these toxic exhaust gases, such as SiH.sub.4, and SiH.sub.2 Cl.sub.2, is to heat the exhaust gases to about 800.degree. C. and to mix them with oxygen gas at high temperature to form a waste powder of SiO.sub.2 compounds. The high temperature compounds then mix with cooling water to form a waste powder containing vapor and waste water for discharging. An exhaust gas treatment apparatus usually has to perform the function set forth above to handle the exhaust gases generated in the diffusion and deposition processes.
FIG. 1 illustrates a conventional exhaust gas treatment apparatus 10 which includes a main pipe 12, an U pipe 14 and a discharge pipe 16.
The main pipe 12 includes an inlet 121 at an upper end thereof, an outlet 122 at a lower end, a heater 123 surrounding the main pipe 12, a sprinkler 124 consisting of a plurality of nozzles and being located at a lower portion of the main pipe 12 in the center for providing cooling water required for exhaust gas treatment, and a scraper 125 which has a plurality of scraping knives located at the inside wall of the main pipe 12. The scraper 125 is driven by a transmission means 126 for removing lump type exhaust gas powder 20 adhering to the inside wall of the main pipe 12.
The U pipe 14 includes a pipe body 143, a first connector 141 located at one end of the pipe body 143 and connected with a bottom end of the main pipe 12, a second connector 142 located at another end of the pipe body 143, and a drain 144 located below the second connector 142.
The discharge pipe 16 has a bottom end connecting with the second connector 142, filters 161 located inside for filtering exhaust gas, and a suction motor 162 to speed up exhaust gas treatment process.
Exhaust gases generated in the diffusion and deposition processes flow in the main pipe 12 through the inlet 121, are heated by the heater 123 to form high temperature exhaust gas powders after having reaction with oxygen gas. The exhaust gases powder are then cooled by cooling water from the sprinkler 124 to form waste powder containing vapor and waste water which enter into the U pipe 14 through the outlet 122 and the first connector 141. Vapor continues to flow through the second connector 142 and is discharged out through the discharge pipe 16. Waste water is discharged out through the drain 144.
However, when vapor and waste water that contain waste powder enter into the U-pipe 14, some of the vapor may be reflux into the main pipe 12. Waste powder contained in the vapor will accumulate around the outlet 122 and consequently shrink the diameter of the outlet 122. Furthermore, the lump type waste powder scraped from the inside wall of the main pipe 12 by the scraper 125 drops down to and easily clogs the U-pipe 14. All this makes exhaust gas discharge inefficient or difficult. Hence an exhaust gas treatment apparatus needs periodic preventive maintenance to clear the waste powder accumulated around the outlet 122 and in the U-pipe 14. The preventive maintenance frequency is usually two to four times per week. The time and frequency needed for preventive maintenance of an exhaust gas treatment apparatus becomes a serious drag on wafer production efficiency. An improvement in exhaust gas treatment can greatly enhance wafer production efficiency.